1. Field of the Invention
The present invention relates to an electric horn employed in a vehicle; and more particularly, to a spark free circuit of an electric horn capable of minimizing or removing an electric arc produced between the mechanical contacts in a horn actuating circuitry during the operation of the horn.
2. Prior Art
In general, an electric horn for use in a vehicle includes a horn actuating circuitry having mechanical contacts arranged therein. A typical electric horn has an interrupter connected serially in circuit with a coil of an electromagnet. Therefore, electric arc may be produced at the interface between the contacts of the interrupter especially when a high current, e.g., 5 amperes, flows through the serial connection of the interrupter and the coil of the electromagnet. Such an arcing condition induces an electromagnetic interference that may disturb or interfere with radio reception and affect adversely on the operation of the other electronic control circuits in the same vehicle.
Furthermore, such electric arc may result in burning-out on fusing-down of the contacts. This requires use of an expensive and high durability material in constructing the interrupter.
For example, as shown in FIG. 1, the electric horn comprises a diaphragm 10 held at its peripheral portion in a house of the horn having an armature 12 attached to a middle portion thereof, an electro-magnet 14 having a coil 16 and disposed adjacent to the armature 12 for causing the armature 12 to move downward under a magnetic field of the electromagnet 14, an interrupter 24 having a pair of normally-closed contacts 26 and 28 and connected at the contact 28 to a DC power source 18, the contacts 26 and 28 being opened by the downward movement of the armature 12, and a horn actuating witch 30 connected serially to the contact 26.
Accordingly, there have been proposed electric horns for suppressing such electric arc. For example, U.S. Pat. No. 4,568,995 discloses an electromagnetic interference suppression device for suppressing electric between the mechanical contacts of a vehicle horn actuating circuit. However, such device has a disadvantage in that there is not provided means for controlling an electric current to be supplied to the contacts at an appropriate level. Therefore, it has limited effectiveness in reducing the electric arc occurring at the mechanical contacts.
In Japanese Laid-Open Patent Publication No. 86-200045, there is provided an electric alarm capable of diminishing electric arc produced between the contacts of an interrupter during the operation of the alarm. However, in this device, since a horn actuating switch is connected serially in circuit with a coil of an electromagnet, a large quantity of current flows through the horn actuating switch, thereby creating an electric arcing condition at the interface between the contacts of the horn actuating switch.
On the other hand, in order to remove the electric arc across the contacts of the horn actuating switch, a horn relay may be used to channel a small quantity of current through the horn actuating switch. However, such addition of a horn device and a relatively high manufacturing cost. Furthermore, since the electromagnet is situated near the foremost of a vehicle, while the horn relay is located near the horn actuating switch which is positioned within a steering wheel, a lengthy conductor is required to connect the electromagnet with the horn actuating switch. As a result, the conductor acts as a source of an electromagnetic interference which frequently occurs from a high frequency signal, e.g., 400 Hz of 5 amperes, flowing therethrough, thereby disturbing or interfering with other electronic controls.
Accordingly, it is an object of the present invention to provide a sparking free circuit of an electric horn employed in a vehicle, which can remove or minimize an electric arc produced between the mechanical contacts of a horn actuating switch during the operation of the horn.
It is another object of the present invention to provide a sparking free circuit of an electric horn capable of reducing the current flowing through a horn switch with the electronic noise.
It is another object of the present invention to provide a sparking free circuit of an electric horn capable of producing soft sounds.
According to the present invention, there is provided an electric horn which comprises:
a diaphragm held at its peripheral portion in a housing of the horn and having an armature attached to a middle portion thereof;
an electromagnet having a coil and disposed adjacent to the armature in an opposed relationship with each other for causing the armature to move down under an action of a magnetic field produced by an energizing current flowing through said coil;
an interrupter having a pair of normally-closed contacts including a fixed contact and a movable contact and connected at one contact to a DC power source;
a horn actuating switch connected serially in circuit with the interrupter; and
a sparking free circuit comprising;
at least one electronic triggering switching means connected to the coil, for interrupting the energizing current supply to the coil of the electromagnet;
the normally-closed interrupter located near the armature and connected to a control input of the triggering switching means, for turning ON and OFF the triggering switching means, the movable contact engaging the armature so as to open the interrupter by the downward movement of the armature;
a current limiting means connected serially with the interrupter.
A capacitor is connected in parallel with the horn actuating switch for enabling the turning ON and OFF cycle of the triggering switching means to be repeated in a given period of time during which the electric current flowing through the coil of the electromagnet is gradually reduced in its level.